1. Field of the Invention
The present invention relates to a member for brakes in large ground transport machines, for example, an installed member for brakes which is connected with a speed control device and used as the friction material of brake discs for speed control or stopping of a large class automobile.
2. Related Art Statement
Composite Carbon Fiber (hereinafter referred to as xe2x80x9cC/Cxe2x80x9d), which is lightweight and presently known to have an extremely high coefficient of friction under the conditions of high temperatures, is widely used as a friction material that is connected to a controlling device for a large class automobile such as a large ground transport machine.
Depending on changes in driving conditions, long continuous periods of braking or frequent pumping of the brakes may be necessary in order to stop these types of large ground transport machines. As such, in the case where C/C is used as a friction material in the braking device, that braking device will be operating under high temperature for long periods of time in an open atmosphere. Therefore, because carbon fiber, which generally burns easily at high temperatures, is used as the main component for these friction materials, cases have been reported where under such conditions a reaction with oxygen occurs and not only do the friction materials undergo remarkable wear, but they cause smoke, which, as it has been reported, has come just before big accidents have occurred. However, presently there are no known substitute raw materials available when considering the high frictional power which occurs under high temperatures and the efficiency of flexibility and the like which is required at the moment the disc brake is applied.
It is an object of the present invention to, provide frictional materials for brakes which maintain the C/C composite""s excellent features of shock resistance and light weight, and provide frictional materials for brake usage. It is a further object of the present invention to provide frictional materials for brake usage which, even in the case where frictional materials for the brakes of large ground transport machines were used, are capable of avoiding the current need for frequent changes in brake pads, since as in the C/C composite, in an oxygen environment and under high temperatures, inevitably severe wear will occur.
The inventors have studied intensively and have found that the above-mentioned aim can be attained by using a fiber-composite material which maintains the excellent features of shock resistance and light weight, and is able to sufficiently withstand wear in an oxygen environment where high temperatures occur and where other disc brake frictional materials would have broken down, and where frequent replacement, such as are necessary with the C/C composite, are not necessary, and intermittent use is possible. This fiber-composite material is prepared by a yarn, including at least a bundle of carbon fiber and a carbon component other than carbon fiber, which is three-dimensionally combined and integrally formed so as to avoid separation of the carbon fiber bundle and the carbon component, into an assemblage of yarns. The space between the adjacent yarn is then filled with a matrix made of Sixe2x80x94SiC-based material. The present invention has been completed based on the above mentioned finding.
The fiber composite material used to make the frictional material for brakes (hereinafter sometimes only referred to as a member for brakes) of the present invention, is unitarily formed into the spaces of the assemblage of yarns derived from carbon fiber, which is three-dimensionally combined and integrally formed so as to avoid separation, by a matrix derived from Sixe2x80x94SiC-based material. In the hereinafter stated case where layers of the matrices formed from Sixe2x80x94SiC-based material are provided, the thickness of the layer is preferably 0.01 mm or more, more preferably 0.05 mm or more, and most preferably 0.1 mm or more.
Additionally, for said fiber composite material used to make the frictional material for brakes, said matrix has an inclined composition in which the content rate of silicon becomes higher in proportion to its distance from the above stated yarn. Also, either one, two, or more of boron nitride, boron, copper, bismuth, titanium, chrome, tungsten, or molybenum can be included in said fiber composite material. Further, at normal temperature the dynamic coefficient of friction for the above stated frictional material for brakes is preferably 0.05xcx9c0.06 and as the temperature rises, it is preferable for the dynamic coefficient of friction to rise correspondingly.